The name "argon" is derived from the Greek word αργον, neuter singular form of αργος meaning "lazy" or "inactive", as a reference to the fact that the element undergoes almost no chemical reactions. The complete octet (eight electrons) in the outer atomic shell makes argon stable and resistant to bonding with other elements. Its triple point temperature of 83.8058 K is a defining fixed point in the International Temperature Scale of 1990.

Argon has approximately the same solubility in water as oxygen, and is 2.5 times more soluble in water than nitrogen. Argon is colorless, odorless, nonflammable and nontoxic as a solid, liquid, and gas.[7] Argon is chemically inert under most conditions and forms no confirmed stable compounds at room temperature.

Although argon is a noble gas, it has been found to have the capability of forming some compounds. For example, the creation of argon fluorohydride (HArF), a compound of argon with fluorine and hydrogen which is stable below 17 K, was reported by researchers at the University of Helsinki in 2000.[8][9] Although the neutral ground-state chemical compounds of argon are presently limited to HArF, argon can form clathrates with water when atoms of it are trapped in a lattice of the water molecules.[10] Argon-containing ions and excited state complexes, such as ArH+ and ArF, respectively, are known to exist. Theoretical calculations have predicted several argon compounds that should be stable,[11] but for which no synthesis routes are currently known.

Lord Rayleigh's method for the isolation of argon, based on an experiment of Henry Cavendish's. The gases are contained in a test-tube (A) standing over a large quantity of weak alkali (B), and the current is conveyed in wires insulated by U-shaped glass tubes (CC) passing through the liquid and round the mouth of the test-tube. The inner platinum ends (DD) of the wire receive a current from a battery of five Grove cells and a Ruhmkorff coil of medium size.

Argon (αργον, neuter singular form of αργος, Greek meaning "inactive", in reference to its chemical inactivity)[12][13] was suspected to be present in air by Henry Cavendish in 1785 but was not isolated until 1894 by Lord Rayleigh and Sir William Ramsay at University College London in an experiment in which they removed all of the oxygen, carbon dioxide, water and nitrogen from a sample of clean air.[14][15][16] They had determined that nitrogen produced from chemical compounds was one-half percent lighter than nitrogen from the atmosphere. The difference seemed insignificant, but it was important enough to attract their attention for many months. They concluded that there was another gas in the air mixed in with the nitrogen.[17] Argon was also encountered in 1882 through independent research of H. F. Newall and W. N. Hartley. Each observed new lines in the color spectrum of air but were unable to identify the element responsible for the lines. Argon became the first member of the noble gases to be discovered. The symbol for argon is now "Ar", but up until 1957 it was "A".[18]

Argon is notable in that its isotopic composition varies greatly between different locations in the Solar System. Where the major source of argon is the decay of 40K in rocks, 40Ar will be the dominant isotope, as it is on Earth. Argon produced directly by stellar nucleosynthesis, in contrast, is dominated by the alpha process nuclide, 36Ar. Correspondingly, solar argon contains 84.6% 36Ar based on solar wind measurements,[23] and the ratio of the three isotopes 36Ar : 38Ar : 40Ar in the atmospheres of the outer planets is measured to be 8400 : 1600 : 1.[24] This contrasts with the abundance of primordial36Ar in Earth's atmosphere: only 31.5 ppmv (= 9340 ppmv × 0.337%), comparable to that of neon (18.18 ppmv); and with measurements by interplanetary probes.

The Martian atmosphere contains 1.6% of 40Ar and 5 ppm of 36Ar. The Mariner probe fly-by of the planetMercury in 1973 found that Mercury has a very thin atmosphere with 70% argon, believed to result from releases of the gas as a decay product from radioactive materials on the planet. In 2005, the Huygens probe discovered the presence of exclusively 40Ar on Titan, the largest moon of Saturn.[21][25]

The electronic properties (ionization and/or the emission spectrum) are necessary.

Other noble gases would probably work as well in most of these applications, but argon is by far the cheapest. Argon is inexpensive since it occurs naturally in air, and is readily obtained as a byproduct of cryogenicair separation in the production of liquid oxygen and liquid nitrogen: the primary constituents of air are used on a large industrial scale. The other noble gases (except helium) are produced this way as well, but argon is the most plentiful by far. The bulk of argon applications arise simply because it is inert and relatively cheap.

Argon is used in some high-temperature industrial processes, where ordinarily non-reactive substances become reactive. For example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning.

Argon is used in the poultry industry to asphyxiate birds, either for mass culling following disease outbreaks, or as a means of slaughter more humane than the electric bath. Argon's relatively high density causes it to remain close to the ground during gassing. Its non-reactive nature makes it suitable in a food product, and since it replaces oxygen within the dead bird, argon also enhances shelf life.[citation needed][32]

Liquid argon is used as the target for neutrino experiments and direct dark matter searches. The interaction of a hypothetical WIMP particle with the argon nucleus produces scintillation light that is detected by photomultiplier tubes. Two-phase detectors also use argon gas to detect the ionized electrons produced during the WIMP-nucleus scattering. As with most other liquefied noble gases, argon has a high scintillation lightyield (~ 51 photons/keV[33]), is transparent to its own scintillation light, and is relatively easy to purify. Compared to xenon, argon is cheaper and has a distinct scintillation time profile which allows the separation of electronic recoils from nuclear recoils. On the other hand, its intrinsic beta-ray background is larger due to 39Ar contamination, unless one uses underground argon sources which has much less 39Ar contamination. Most of the argon in the Earth’s atmosphere was produced by electron capture of long-lived 40K (40K + e− → 40Ar + ν) present in natural potassium within the earth. The 39Ar activity in the atmosphere is maintained by cosmogenic production through 40Ar(n,2n)39Ar and similar reactions. The half-life of 39Ar is only 269 yr. As a result, the underground Ar, shielded by rock and water, has much less 39Ar contamination.[34] Dark matter detectors currently operating with liquid argon include DarkSide, WArP, ArDM, microCLEAN and DEAP-I. Neutrino experiments include Icarus and MicroBooNE both of which use high purity liquid argon in a time projection chamber for fine grained three-dimensional imaging of neutrino interactions.

Argon is used to displace oxygen- and moisture-containing air in packaging material to extend the shelf-lives of the contents (argon has the European food additive code of E938). Aerial oxidation, hydrolysis, and other chemical reactions which degrade the products are retarded or prevented entirely. Bottles of high-purity chemicals and certain pharmaceutical products are available in sealed bottles or ampoules packed in argon. In wine making, argon is used to top-off barrels to avoid the aerial oxidation of ethanol to acetic acid during the aging process.

Argon is also available in aerosol-type cans, which may be used to preserve compounds such as varnish, polyurethane, paint, etc. for storage after opening.[35]

Argon may be used as the inert gas within Schlenk lines and gloveboxes. The use of argon over comparatively less expensive nitrogen is preferred where nitrogen may react with the experimental reagents or apparatus.

Cryosurgery procedures such as cryoablation use liquefied argon to destroy tissue such as cancer cells. In surgery it is used in a procedure called "argon enhanced coagulation" which is a form of argon plasma beamelectrosurgery. The procedure carries a risk of producing gas embolism in the patient and has resulted in the death of one person via this type of accident.[37]

Blue argon lasers are used in surgery to weld arteries, destroy tumors, and to correct eye defects.[21]

Argon has also been used experimentally to replace nitrogen in the breathing or decompression mix known as Argox, to speed the elimination of dissolved nitrogen from the blood.[38]

Argon has been used by athletes as a doping agent to simulate hypoxic conditions. On August 31 2014 the World Anti Doping Agency (WADA) added argon and xenon to the list of prohibited substances and methods, although at this time there is no reliable test for abuse.[42]

Although argon is non-toxic, it is 38% denser than air and is therefore considered a dangerous asphyxiant in closed areas. It is also difficult to detect because it is colorless, odorless, and tasteless. A 1994 incident in which a man was asphyxiated after entering an argon filled section of oil pipe under construction in Alaska highlights the dangers of argon tank leakage in confined spaces, and emphasizes the need for proper use, storage and handling.[43]